A bag contains five white balls and four black balls. Your goal is to draw two black balls.
b)You draw two balls at random. Once you have drawn two balls, you put back any white balls, and redraw so that you again have two drawn balls. What is the probability that you now have two black balls? (Include the probability that you chose two black balls on the first draw.)
I got 89/216, but it said it was wrong. What is going on??
You must consider the probability that drawing BB, BWB, WWB, or WWBB. This gives you a probability of 2/9 + 5/81 + 12/81 + 6/81 = 41/81.